Rhinotocinclus acuen ( Silva, Roxo & Oliveira, 2014 ), 2022

Rhinotocinclus acuen ( Silva, Roxo & Oliveira, 2014) , new combination

( Fig. 44 View FIGURE 44 ; Tab. 9 View TABLE 9 )

Hisonotus acuen Silva, Roxo & Oliveira, 2014:107 (Type-locality: Brazil, Mato Grosso State, municipality of Querência, affluent of rio Toguro, rio Xingu basin, 13°00’26”S 52°11’27”W. Holotype: MZUSP 115350).

Diagnosis. Rhinotocinclus acuen is distinguished from congeners, except R. chromodontus , R. jumaorum , and R. dinizae , by having the dominant color pattern formed by a dark stripe from the snout tip, through the eye and extending to end of caudal peduncle (Fig. 7E; vs. dominant color pattern formed by dark bars separated and distinct, or dark bars wide and partially coalesced or closed together), and by having a V-shaped light mark from the snout tip to each nostril (Figs. 6C,D; vs. light mark absent, Y-shaped or present as two separate lines from snout tip diverging to each nostril). It is also distinguished from congeners, except R. chromodontus , R. dinizae , R. hera , and R. jumaorum , by lacking an adipose fin or platelets at the adipose-fin position ( vs. adipose fin or platelets present). Rhinotocinclus acuen is distinguished from R. chromodontus by having oral teeth light ochre (Fig. 5B; vs. teeth reddish brown), caudal fin with a dark blotch at the base and two irregular dark bands ( vs. caudal fin mostly brown, with two hyaline spot on upper and lower lobes), the dorsal- and pectoral-fin spines with 2–3 dark dots ( vs. spines homogeneously dusky), narrower body (cleithral width 21.7– 24.1% vs. 24.9–27.9% SL and 57.6–62.7% vs. 67.7–76.2% HL), and fewer teeth (17–22 premaxillary, 14–19 dentary; vs. 26–40 and 21–34, respectively). It is distinguished from R. jumaorum by having teeth light ochre ( vs. teeth brown), and by the relative proportion of caudal peduncle depth and body width (caudal peduncle depth 39.2–45.0% vs. 35.4– 39.0% cleithral width). Rhinotocinclus acuen is distinguished from R. dinizae by having shorter fins (dorsal-fin spine 20.0–22.8% vs. 22.8–25.5% SL, anal-fin unbranched ray 15.0–17.4% vs. 18.5–19.5% SL, and pectoral-fin spine 23.1–26.9% vs. 28.1–30.0% SL), and a shorter head (head length 37.0–40.0% vs. 40.0–41.8% SL).

Geographical distribution. Rhinotocinclus acuen occurs in the tributaries of the upper rio Xingu in the state of Mato Grosso, Brazil ( Fig. 43 View FIGURE 43 ).

Remarks. Rhinotocinclus acuen was also described as a member of Hisonotus , and accordingly compared to other species of the later genus ( Silva et al., 2014). Interestingly, in the diagnosis of the new species the authors begin saying “ Hisonotus acuen differs from all congeners except H. bockmanni , H. chromodontus , H. insperatus , H. luteofrenatus , H. oliveirai , and H. paresi by having a functional V-shaped spinelet”. Both H. bockmanni and H. chromodontus are herein being tranferred to Rhinotocinclus and the remaining species have already been transferred to Curculionichthys , the functional V-shaped spinelet indeed diagnosing R. acuen and, in fact, all Rhinotocinclus and Curculionichthys species, from Hisonotus . Extintion risk of Rhinotocinclus acuen is currently not assessed.

Material examined. Rio Xingu basin, Mato Grosso State, Brazil: MZUSP 115350 , holotype (measured), creek tributary to rio Toguro , Querência, 13°00’26”S 52°11’27”W GoogleMaps . MCP 40543 , 22 (5 measured), AUM 73894, 10 , INPA 59665, 10 , ROM 111486, 10, córrego Trinta, tributary to rio Suaizinho on road BR-153 between Alô Brasil and Ribeirão Cascalheira, Ribeirão Cascalheira, 12°14’54”S 51°42’45”W. GoogleMaps MCP 32671, 2, creek tributary to rio Azul on road MT-140, Santa Carmen, 11°59’55”S 55°16’39”W. GoogleMaps MCP 32672, 5, rio Ferro on road from Novo Mato Grosso to Nova Ubiratã, ca. 25 km SW of Novo Mato Grosso, Nova Ubiratã, 13°03’32”S 55°02’12”W. GoogleMaps MCP 32673, 10 (3 measured) + 2 cs, creek tributary to rio da Saudade on road MT-423, ca. 38 km SE of Marcelândia, Analândia do Norte, 11°13’23”S 54°17’24”W GoogleMaps . MCP 32679, 2, córrego Tatu on road MT- 423, 14 km W of Cláudia, Cláudia, 11°28’36”S 54°58’47”W GoogleMaps . MCP 32680, 1, córrego Saudade on road from Santa Helena to Marcelândia, 66 km SE of road BR-163, Marcelândia, 11°07’07”S 54°40’15”W. GoogleMaps MCP 32681, 3, ribeirão Camparina on road MT-320 from Santa Helena to Marcelândia, 79 km SE of road BR-163, Marcelândia, 11°06’27”S 54°33’03”W GoogleMaps . MCP 32682, 9, rio Azul on road MT-140, ca. 7 km NNW of Santa Carmen, Santa Carmen, 11°54’42”S 55°17’48”W GoogleMaps . MCP 32683, 3, creek on road from Santa Terezinha to Iberê, ca. 10 km W of Iberê, Nova Ubiratã, 12°45’19”S 54°34’25”W GoogleMaps . MCP 32684, 7 + 1 cs, creek tributary to rio Tartaruga on road from Vera to Feliz, Vera, 12°15’55”S 55°15’37”W GoogleMaps . MCP 32685, 3, rio Azul on road MT- 423, 16 km w of Cláudia, Cláudia, 11°28’20”S 54°59’40”W GoogleMaps . MCP 32686, 6, rio Tartaruga on road MT-423 ca. 20 km E of Vera, Cláudia, 11°30’36”S 54°42’43”W. GoogleMaps MCP 32687, 16, creek on road from Novo Mato Grosso to Nova Ubiratã, 7 km SW of Novo Mato Grosso, Nova Ubiratã, 12°57’10”S 54°54’46”W GoogleMaps . MCP 32688, 3, rio Tartaruga at Nova Ubiratã, Nova Ubiratã, 13°02’03”S 55°16’07”W. GoogleMaps MCP 32689, 1, creek on road MT-320 from Santa Helena to Marcelândia, 73 km SE of road BR-163, Marcelândia, 11°07’39”S 54°36’52”W GoogleMaps . MCP 32690, 6, rio da Saudade on road MT- 423, 31 km SE of Marcelândia, Marcelândia, 11°11’11”S 54°19’27”W GoogleMaps . MCP 32691, 2, creek on road MT- 423, 22 km SE of Marcelândia, Marcelândia, 11°12’21”S 54°23’19”W. GoogleMaps MCP 32692, 4, creek tributary to rio Tartaruga on road from Novo Mato Grosso to Nova Ubiratã, ca. 44 km WSW of Novo Mato Grosso, Nova Ubiratã, 13°02’43”S 55°12’21”W. GoogleMaps MCP 32693, 2, rio Von der Steinen (or Atelchu) on road from Santa Terezinha to Iberê, ca. 28 km W of Iberê, Nova Ubiratã, 12°47’05”S 54°40’49”W. GoogleMaps MCP 32694, 6, creek tributary to rio Manissamá-Miçu on road MT-423 ca. 11.6 km SE of Marcelândia, Marcelândia, 11°09’46”S 54°27’01”W. GoogleMaps MCP 32695, 2, rio Tartaruga on road from Vera to Feliz Natal, 20 km NE of Vera, Vera, 12°14’21”S 55°07’11”W. GoogleMaps MCP 32696, 4, creek ca. 2 km N of Novo Mato Grosso, Nova Ubiratã, 12°53’49”S 54°50’54”W GoogleMaps . MCP 40283, 45 , MHNG 2787.080, 10, rio Traíras ca. 3 km W of Posto da Mata on road BR 242, Posto da Mata, 11°42’40”S 51°39’18”W GoogleMaps . MCP 40299, 12, córrego da Caaporã, tributary to córrego Três Marias, rio Suiazinho on road BR-158, Ribeirão Cascalheira, 12°32’10”S 51°46’45”W GoogleMaps . MCP 40365, 16 (2 measured), creek N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°35’50”S 51°46’55”W GoogleMaps . MCP 40402, 23, creek tribuatry to rio Suiazinho on road BR-158, ca. 1 km N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°29’21”S 51°46’06”W GoogleMaps . MCP 40720, 10, creek tributary to rio Suiazinho on road BR 158, ca. 1 km N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°29’21”S 51°46’06”W GoogleMaps . MCP 40732, 18, córrego Trinta, tributary to rio Suaizinho on road BR-153 between Alô Brasil and Ribeirão Cascalheira, Ribeirão Cascalheira, 12°14’54”S 51°42’45”W GoogleMaps . MCP 40790, 5, creek N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°35’50”S 51°46’55”W. GoogleMaps MCP 40814, 5, rio Traíras ca. 3 km W of Posto da Mata on road BR-242, Posto da Mata, 11°42’40”S 51°39’18”W. GoogleMaps